6 Common Tree Diseases and Pests Explained

Just like people, trees are vulnerable to diseases and affliction. A diseased tree can not only be unattractive, but can also infect other trees and plants surrounding it, causing problems in the ecosystem. It’s important to take action as soon as possible if you notice that a tree is becoming infected. Here is a list of some of the most common tree diseases and the pests that cause them, and how you can spot them.

1. Emerald ash borer

A beetle called the Emerald Ash Borer might be causing problems with your tree if you notice the leaves turning yellow before autumn, after which the branches die. The beetle digs into the bark of the tree and infects it while building tunnels throughout. As its name would suggest, this bug affects all species of ash trees. There are fungicides that can be injected into the tree to prevent infection, but they are not completely reliable. Unfortunately, the only way to “cure” a tree that’s been infected by the emerald ash borer is to remove it completely. This must be done to protect surrounding trees and vegetation.

2. Cypress canker

This affliction has been running rampant in Australia for the past several years, and unfortunately, there is currently no cure or prevention method for it. Cyprus cankers are caused by an infection carried by water, the wind, or from pruning materials used on several plants. The cankers present as an angry red colour on branches and cause a branch to die quickly, sometimes overnight. The branches become yellow and spores are released through tiny black fungus on the canker. If not caught quickly, the infection can spread to the entire tree and kill it. If a tree is to be removed, it is important not to replace it with another Cyprus, as the new tree would be even more prone to infection. Replace the tree with a non-cyprus tree to avoid further issues.

3. Oak wilt

Oak wilt is a fungus that comes from the soil and is spread by beetles. It is a very fast-acting fungus that can take as little as one growing season to kill a tree. It spreads from oak to oak through the roots, which makes it a little easier to contain and control than other diseases. A tree affected by oak wilt can be spotted by its characteristic wilted leaves that turn rust-coloured during the growing season when they should be a healthy green. Those leaves soon die and fall off the tree well before autumn. Managing the disease is achieved by digging a trench around the affected tree and following appropriate pruning guidelines for preventing oak wilt.

4. Root rot

Root rot, as its name suggests, is another disease caused by fungus that affects the roots through the soil. Once again, wilted leaves during the warm season are a tell-tale sign of root rot. Proper digging and pruning are important for preventing the spread. An interesting thing about root rot is the fungus that causes it is present in pockets of soil, but will not necessarily spread itself out. This means that while one tree may have root rot, another tree close by might not get infected because the soil by the unaffected tree does not have the fungus. This can make controlling root rot simpler than other diseases, although it is still quite common. Usually, a professional is needed to treat it, so if you see wilted leaves on your tree, contact one right away.

5. Citrus gall wasp

Sometimes you might notice the branches of a citrus tree are swelling and bulging. This probably means that the tree has been infected by the citrus gall wasp. The gall wasp lays its eggs in the tree’s branches. The tree’s reaction to the eggs is what causes infection, and also causes the cycle to perpetuate when the new wasps hatch. Gall wasp infections can be controlled by removing the swollen branches before the wasps start spreading to other branches. There are no sprays that are known to control gall wasps, so make sure to cut off those branches as soon as you see signs of swelling.

6. Anthracnose

Anthracnose is a fungus that loves damp spots and hiding under foliage. It can cause problems with growing leaves, holes in the existing leaves, and defoliation as well. If caught soon enough, you can save an affected tree by cutting off and burning any foliage that looks infected. Since anthracnose likes damp places, plant trees with enough space for good airflow to keep things as dry as possible.

Disease is a reality for many of beautiful species of trees. Make sure you know the signs so you can protect one of our best friends in nature.